The present invention relates generally to improvements in intercom systems, and more particularly, pertains to new improved subscriber installation intercom systems wherein the intercom system is expandable on a modular basis to accommodate an increasing number of subscriber stations at the installation.
In the field of intercom systems and subscriber installations, it has been the practice to provide intercom systems that will satisfy up to a maximum number of subscriber units. If that number is exceeded, a new intercom system must be installed, and if the number of subscriber stations gets too large, a PBX system would have to be utilized. Besides being static as to the number of subscriber units that prior intercom systems could accommodate, these intercom systems were lacking in the service features that they supplied to the subscriber unit. Most prior intercom systems utilize a single talking loop. Therefore, a single subscriber unit can tie up the entire intercom. Besides these drawbacks, the prior art intercom systems do not provide the services that a PBX system does, such as individual ringing of the intercom units, dial tone, busy tone, and ring back, for example.